1. Field of the Invention
The present invention relates to a method of monitoring ion-implantation process, and a monitoring apparatus using the same. More particularly, the present invention is directed to a method of monitoring an ion-implantation process using photo-thermal response from an ion-implanted sample in order to improve the analysis for process conditions of ion-implantation process, such as ion-dose or ion-implantation energy, by using the frequency response characteristics of the plasma and thermal waves generated by the excitation of the ion-implanted portion, and a monitoring apparatus using the same.
2. Description of Related Art
Generally, in the semiconductor device fabrication process, ion-implantation is carried out in order to implant impurities on a certain active area or insulating area, and change the electrical characteristics of the corresponding areas.
The ion-implantation requires precise setting of process conditions and controls therefor in order to achieve desired electrical characteristics on a semiconductor wafer. In general, the dose on the ion-implanted sample and the uniformity of the ion-implantation are the main factors for setting the process conditions and the controls therefor exactly.
Conventionally, the ion-dose and the uniformity are detected by measuring sheet resistivity. This method requires the performance of an annealing process after implanting ions on the wafer. However, the annealing process takes lots of time, and the above measurement method cannot be applied on the wafer having a specific pattern formed thereon.
In order to address these problems, the inspection method for the ion-dose and the uniformity using a photo-thermal response technology was newly introduced, and the U.S. Pat. No. 4,632,562 and the U.S. Pat. No. 5,408,327 disclose the analysis of a sample using photo-thermal response technology, both of which are hereby incorporated by reference in their entirety.
In the photo-thermal response technology, if a modulated laser beam is absorbed on the ion-implanted sample, plasma and thermal waves are generated by excitation of the sample. At this time, frequency differences between the two waves occur, which is used in the analysis for the ion-implantation process.
In other words, during the ion-implantation, damage often occurs on the surface of the sample according to the dose of the impurities and the energy. If a modulated laser beam is irradiated on the surface of the sample for the analysis of the ion-implantation process, a modulated laser beam is absorbed on the damaged portion, and plasma and thermal waves are generated by excitation. The generated plasma and thermal waves change the reflectivity of the surface of the wafer, and the detected results, i.e., the response characteristics, have phase shifts representing a time delay between the amplitude of the changed reflectivity and the excitation.
The response characteristics are measurement parameters for analyzing the dose for the sample and the uniformity, with "K" as the plasma wave parameter, and "R" as the reflectivity parameter are derived from the response characteristics, which are used for the analysis. The thermal wave parameter is K (complex conversion coefficient), which is used for the analysis of ion-dose.
In the analysis using the K (complex conversion coefficient), the amplitude and the phase shift of the K (complex conversion coefficient) according to the variance of the ion dose show a certain range which can be seen as curve-shape as a second-order function graph. However, it is difficult to judge the process conditions for controlling the ion dose precisely just by means of the above graph for K (Complex Conversion Coefficient) with the curve-shape as described above. Fine variations in the signal corresponding to the imaginary part of the curve may cause a great difference in the variance of the ion dose corresponding to the real part thereby making it difficult to precisely analyze.
Therefore, the measurement of the dose of the implanted ions using the above method cannot be accurately applied in the analysis for the ion-implantation and the facility.